| Abstract: | ![]()
Stimulus frequency, intensity, interstimulus interval, and risetime were evaluated for their influence on the acoustic startle reflex, determined by behavioral and EMG techniques, and on the activity of multiple-unit clusters in subdivisions of the mouse inferior colliculus. Tones of 5, 10, and 20 kHz were capable of eliciting the startle response when presented at 80-dB SPL intensities, 5-ms rise time, and variable intervals. The most effective frequency was 10 kHz. Changing the parameters to either 70 dB SPL, 20-ms rise time, or fixed intervals each resulted in a reduced startle response. Discharge rates of most unit clusters in the ventrolateral division of the central nucleus were not reduced under these conditions. By contrast, many clusters in the pericentral and external nuclei showed reduced responsiveness to fixed interval schedules and 20-ms rise time. Some correspondence between the limited effectiveness of 20-kHz tones in eliciting the startle response and the relatively poor 20-kHz responses of neurons in the pericentral and external nuclei was noted. In general, increasing stimulus intensity from 70 to 80 dB produced an increase in the number of discharges evoked in all inferior colliculus subdivision. It is proposed that a pathway mediating the acoustic startle response is likely to include a projection from the ventrolateral division to the pericentral and/or external nuclei and ultimately to motor neurons. |
